Fixes #4045: Repository name and label validations properly handled.

Repository name and label validation were being handled improperly
and without the same format as other model validations. This creates
and proper active record validators for each and provides a message
indicating to the user the scope of the validation (i.e. Product).
Merge pull request #4274 from ehelms/fixes-4045

Fixes #4045: Repository name and label validations properly handled.